In the oil industry, down hole pumps, usually driven from the surface, are used to remove hydrocarbon-based fluid from the well.
There are basically two types of mechanically actuated submersible pumps presently being used in the oil industry: tubing pumps and rod pumps. The operating principal is the same for both, although they differ somewhat in construction and application. Both are positive displacement type pumps. They consist of a cylindrical barrel in which a hollow plunger and a standing (inlet) valve and a travel (exhaust) valve within the plunger; and raise the crude oil from below the ground to the surface. The force necessary to move the plunger is transferred from the surface pumping unit through a string of sucker rods to the pump which is set into the producing formation at or near the bottom of the hole.
A tubing pump is an integral part of the tubing string. The pump barrel serves as a section of tubing. The plunger and traveling valve are run in the well with the sucker rods. The standing valve can be one of two types, either fixed or retrievable. The fixed type is attached below the pump barrel as part of the tubing string. The retrievable type standing valve rests in a cup-type or mechanical-type seating nipple at the bottom of the tubing string. This type can be removed with the sucker rod string by means of a valve puller which is permanently attached to the lower end of the plunger.
Tubing pumps are regarded as high volume, heavy duty pumps. Maximum production can be expected with this type in relation to size of the tubing. However, because of the large plunger diameter, the fluid load will be greater than with a rod pump. Therefore, depending on the rod strength and size of surface pumping equipment, the depth at which the tubing pump can be run is limited.
When barrel repairs are required on the tubing pump, the entire tubing string must be pulled. This is a more expensive operation than a simple rod pulling job to repair and insert a rod pump.
Rod pumps are inserted inside the well tubing and run as an assembled unit with the sucker rods. Rod pumps have a cup-type or mechanical-type seating nipple which is run as part of the tubing string. A rod pump is removed from the tubing when the sucker rod string is pulled.
A rod pump is necessarily smaller in diameter than a tubing pump and, therefore, of smaller capacity for given tubing size.
The American Petroleum Institute (API) classifies pump by size, and by rod or tubing type pumps. In addition, pumps are classified as either heavy wall or thin wall pumps. Pumps may be either metal to metal pumps, or soft type pumps. Metal to metal pumps are made with a precision-honed barrel and a metal plunger. The tolerance between the barrel and the plunger (plunger clearance) can be specified to achieve the greatest volume metric efficiency and the longest possible pump life under given well conditions.
Steel, brass and monel barrels are available plain or chrome-plated interior diameters to reduce friction and improve pump life. Hardened steel, to help overcome medium to severe abrasion, is also available. Steel plungers can be spray coated with wear-resistant alloy materials to help reduce corrosion and wear.
Soft-packed pumps seal the barrel to plunger with cups, rings or repacks, or combination of these. Soft-packed pumps are generally not recommended for use below 5,000 feet because the fluid load in deeper wells.
Typical rod and tubing pumps currently used in the oil industry may be found in the Dover Corporations Norris O'Bannon Pump Catalog, P.O. Box 2070, Tulsa, OK 74101. This catalog also contains an illustration and explanation of how a subsurface pump works.
A typical hydraulically actuated subsurface pump unit comprises a single-acting pump powered by a hydraulic motor, with the hydraulic motor receiving its motor force from high pressure oil pumped down the well to the motor. In general, the hydraulic motor comprises a differential area piston having its smaller end continuously exposed to high pressure power drive fluid and a main valve in the piston for controlling the flow of power fluid to the larger end of the piston, while the piston is reciprocating within the cylinder. The main valve is in turn controlled by a pilot valve, with the pilot valve usually being carried in the piston and mechanically shifted by the piston to open one or more ports which, in turn, hydraulically shift the main valve.
Kobe Hydraulic oil well pumping systems manufactures a double acting, double cylinder-double piston down hole hydraulically (water or oil) driven pump. This pump may be used in open or closed power fluid systems and comes in a variety of piston sizes to meet all depth and volume requirements, but requires high operating pressures and high r.p.m.'s to drive the pump. Further, the Kobe pump uses lube oil as the hydraulic fluid and not a portion of the formation fluid.
A number of patents disclose a double-piston and double-cylinder pump driven by hydraulic fluid.
U.S. Pat. No. 2,366,777 (Farley 1945) discloses a hydraulic pump with two pistons connected by a common connecting rod. Each piston reciprocates in its own cylinder. The pump uses fluid pressure to drive sucker rods. Compared with the present invention, Farley's drive piston is raised and lowered by drive fluid pressure that exhausts the drive fluid only on the upstroke. In addition, the valving arrangement is different.
U.S. Pat. No. 2,631,541 (Dempsey 1953) also discloses a pump which is fluid actuated and has a double-piston, single connecting rod structure. The reciprocating drive piston contains a pilot valve to channel the high pressure drive fluid therethrough. Input supply pressure is constantly maintained on one face of the drive piston and exhaust pressure relief is regulated on the opposite face causing the movement of piston in one direction. It diverts spent power fluid through the connecting rod by means of valving in the piston. The Dempsey pump alternates a working stroke with a nonworking stroke.
U.S. Pat. No. 2,943,567 (English 1960) discloses yet another double-piston common connecting rod arrangement. The English pump uses side inlet and outlet ports and contains a valve in piston unit that transfers the drive fluid through the piston and the hollow connecting rod and to the working plunger.
U.S. Pat. No. 3,093,122 (Sachnik 1963) discloses a reciprocating-type piston pump using pressurized fluid to drive the piston. A master slide valve controls the distribution of the pressurized fluid to a power piston that is connected to a piston rod, also common to the fluid pump piston. A pilot slide valve operable upon movement of the common piston rod controls the operation of the master slide valve.
However, none of the prior art pumps disclose the unique valving of the present invention, which eliminates the need for a valve in piston, hollow connecting rods or slide valves. Nor do they disclose a high volume, long stroke, hydraulically driven pump capable of operating at relatively low pressures, and low r.p.m.'s.
The present methods for removing fluids from subsurface producing formations use down hole pumps that are either mechanically activated by sucker rods, are hydraulic drive or are electrically driven (such as Recter pumps). However, those hydraulically driven pumps known in the art require high pressures (over 1000 p.s.i.) which accelerates pump wear and escalates costs.